Synchronous rectifier

1. A synchronous rectifier, comprising: an input unit outputting an alternative input signal and a process signal in response to an AC input signal and a rectifying signal respectively; a control unit electrically connected to said input unit, comprising: a pulse-time control circuit for producing said rectifying signal, a first driving signal, and a second driving signals, comprising: a pulse width modulator receiving said alternative input signal; and an adjustable time-gushing circuit electrically connected to said pulse width modulator; and an output unit electrically connected to said input unit and said control unit, and having a first switch control circuit and a second switch control circuit in response to said first driving signal and said second driving signal respectively for transforming said process signal into an output signal while said first switch control circuit and said second switch control circuit are free for a cross conduction.

2. The synchronous rectifier according to claim 1 , wherein said input unit further comprises: a signal detecting circuit for detecting and inputting said AC input signal, and generating said alternative input signal; and a rectifying circuit electrically connected to said signal detecting circuit and said control unit for rectifying said AC input signal in response to said rectifying signal from said control unit, so as to output said process signal.

3. The synchronous rectifier according to claim 2 , wherein said signal detecting circuit is a current detecting circuit.

4. The synchronous rectifier according to claim 2 , wherein said rectifying circuit includes a plurality transformer units and a plurality of transistors.

5. The synchronous rectifier according to claim 4 , wherein said rectifying circuit includes a first, a second and a third transformer units, and a bridge rectifier having four transistors.

6. The synchronous rectifier according to claim 5 , wherein said first and said second transformers transform said rectifying signal to a gate terminal of said four transistors for producing a gate control voltage.

7. The synchronous rectifier according to claim 5 , wherein said third transformer transforms said AC input signal to said rectifying circuit.

8. The synchronous rectifier according to claim 5 , wherein said four transistors are MOSFETs.

9. The synchronous rectifier according to claim 2 , wherein said input unit further includes a signal amplifying circuit electrically connected to said control unit and said rectifying circuit for amplifying and outputing said rectifying signal to said rectifying circuit.

10. The synchronous rectifier according to claim 9 , wherein said signal amplifying circuit is a current amplifier.

11. The synchronous rectifier according to claim 2 , wherein said adjustable time-pushing circuit cooperates with said pulse width modulator to produce said first and said second driving signals, and said rectifying signal, and adjusts and sets periods of a first and a second pulse times.

12. The synchronous rectifier according to claim 2 , wherein said control circuit further comprises a signal cut-off circuit electrically connected to said signal detecting circuit and said pulse time control circuit for producing said first and said second driving signals in response to said AC input signal in a specific signal state, thereby said first and said second switch control circuits both being introduced to a cut-off state for preventing said synchronous rectifier from an external signal.

13. The synchronous rectifier according to claim 12 , wherein said signal cut-off circuit is a low current cut-off circuit.

14. The synchronous rectifier according to claim 13 , wherein said low current cut-off circuit comprises plural voltage comparators.

15. The synchronous rectifier according to claim 12 , wherein said specific signal state is a low current state.

16. The synchronous rectifier according to claim 12 , wherein said external signal is an inversed current produced by an additional synchronous rectifier parallelly connected to said synchronous rectifier.

17. The synchronous rectifier according to claim 5 , wherein said first and said second switch circuits are a first and a second MOSFETs respectively.

18. The synchronous rectifier according to claim 17 , wherein said first and said second driving signals are respectively inputted into gates of said first and said second MOSFETs for producing gate control voltages.

19. The synchronous rectifier according to claim wherein 17 , wherein said output unit further comprises: a first filtering inductor circuit and a second filtering inductor circuits individually connected to drain terminals of said first and said second MOSFETs; and a filtering capacitor circuit electrically connected to said first and said second filtering inductor circuits, and source terminals of said first and said second MOSFETs, wherein said first and said second filtering inductor circuits and said filtering capacitor circuit rectify and transform said process signal into said output signal in response to a turn on state and a turn off state of said first and said second MOSFETs.

20. The synchronous rectifier according to claim 19 , wherein said first and said second filtering inductor circuits are filtering inductors.

21. The synchronous rectifier according to claim 19 , wherein said filtering capacitor circuit is a wave filter capacitor.

22. The synchronous rectifier according to claim 19 , wherein said output unit further comprises a fourth transformer unit electrically connected to said rectifying circuit, and said first and said second MOSFETs for transforming said process signal to said drain terminals of said first and said second MOSFETs.

23. The synchronous rectifier according to claim 1 , wherein said first driving signal and said second driving signal both have a first and a second state.

24. The synchronous rectifier according to claim 23 , wherein said second driving signal is retained in said second state for a period of a first pulse time and then transformed into said first state while said first driving signal is transformed from said first state into said second state.

25. The synchronous rectifier according to claim 23 , wherein said first driving signal is retained in said second state for a period of a first pulse time and then transformed into said first state while said first driving signal is transformed from said first state into said second state.

26. The synchronous rectifier according to claim 23 , wherein said first state is a high level and said second state is a low level.

27. The synchronous rectifier according to claim 23 , wherein said first state is a low level and said second state is a high level.

28. The synchronous rectifier according to claim 23 , wherein while said process signal is in said first state, said first driving signal is in said second state and said second driving signal is in said first state.

29. The synchronous rectifier according to claim 23 , wherein while said process signal is in said second state, said first driving signal is in said first state and said second driving signal is in said second state.

30. The synchronous rectifier according to claim 23 , wherein said first switch circuit is set in one of a conducted state and a non-conducted state according to one of said first state and said second state of said second driving signal.

31. The synchronous rectifier according to claim 23 , wherein said second switch circuit is set in one of a conducted state and a non-conducted state according to one of said first state and said second state of said first driving signal.

32. A synchronous rectifier, comprising: an input unit outputting an alternative input signal and a process signal in response to an AC input signal and a rectifying signal respectively; a control unit electrically connected to said input unit, comprising: a pulse-time control circuit for producing a rectifying signal, a first driving signal, and a second driving signal, comprising: a pulse width modulator receiving said alternative input signal; and an adjustable time-pushing circuit electrically connected to said pulse width modulator; and an output unit electrically connected to said input unit and said control unit, and having a first switch control circuit and a second switch control circuit in response to said first driving signal and said second driving signal respectively for transforming said process signal into an output signal while said first switch control circuit and said second switch control circuit are free for a cross conduction, wherein said input unit further comprises: a signal detecting circuit for detecting and inputting said AC input signal, and generating said alternative input signal; and a rectifying circuit electrically connected to said signal detecting circuit and said control unit for rectifying said AC input signal in response to said rectifying signal from said control unit, so as to output said process signal.